This project will study the success of axonal regeneration within the central nervous system of the anuran amphibian, Rana pipiens, using anatomical methods. Three different types of experiments will be done. 1) We will study tectospinal axons which do not appear to regenerate after hemisecting or transecting the isthmus rhombencephali (isthmal lesion) and compare the success of regneration with that of optic axons after a similar type of lesion. 2) We will determine whether the success of regeneration of optic axons is related to the absence of available non-optic synaptic sites that might interfere with regeneration. Included in this analysis will be an electron microscopic study of one of the zones denervated by an isthmal lesion to determine whether axonal sprouting occurs. 3) We will determine if the factors guiding regnerating optic axons in the adult frog are different from those guiding axons during development. Methods to be used for tracing regenerating axonal connections include the use of anterograde transport of (3H)-amino acids and the anterograde labeling of axons with horseradish peroxidase (HRP). The HRP procedures will be combined with electron microscopy so that we can determine if regenerating axons which are found in abnormal zones or which remain in the zone of neural injury form synaptic endings in these areas.